Aims: This systematic review and meta-analysis aimed to evaluate the pooled prevalence of molar-incisor hypomineralization (MIH) among children. Methods: Three databases (PubMed, Scopus, and CINAHL) were searched till January 1, 2017, for the prevalence of MIH among children. The heterogeneity of the publications was evaluated using I2 statistics. Two trained reviewers conducted risk of bias assessment with nine item checklist for prevalence studies. Results: Analysis of the included publications revealed a pooled prevalence of 11.24 (confidence interval = 9.23–13.45) with the use of quality effects model. Heterogeneity among the included publications was high. The risk of bias assessment showed that majority of them were in the low-risk category. Conclusions: MIH is a common problem and one in 10 children could be affected by MIH.

Molar incisor hypomineralization (MIH) can be defined as “Hypomineralization of systemic origin from one to four first permanent molars frequently associated with affected incisors.”[1] This condition was known with multiple names, namely, cheese molars or idiopathic enamel hypomineralization or nonfluoride hypomineralization. As discussed previously, it occurs due to a disturbance in one of the stages of amelogenesis thus leading to a qualitative defect.[2]

Studies that have been conducted reported a prevalence ranged from 0.48% to 40.16%.[3],[4] The published studies used a variety of criteria for evaluation of MIH thus making it more complicated to compare the same with different population groups. The most widely used criteria before the congress of the European Academy of Pediatric Dentistry (EAPD)[1] was developmental defects of enamel index and its modification given by Fédération Dentaire Internationale (FDI).[5]

Although many prevalence studies have been reported in the past, there was no attempt to consolidate and report the pooled prevalence using a systematic review and meta-analysis. However, many literature reviews reported various aspects such as age, gender, race, geographic distribution, and etiological agents concerning the prevalence of MIH.[6],[7],[8]

MIH can have serious consequences such as increased dental fear and anxiety in children, plus fragile, and sensitive teeth. These conditions might also lead to decay due to avoidance of brushing and posteruptive enamel breakdown. A thorough knowledge of prevalence and determinants of MIH would help dentists, and oral health-care provider understands the distribution of this condition. Hence, we aimed to systematically review the literature, consolidate, and report pooled prevalence of MIH. The objective of this systematic review and meta-analysis was to evaluate the prevalence of MIH with respect to gender and geographical distribution and to report the pooled prevalence of MIH.

Methods

Selection criteria

Studies published among children where the prevalence of MIH was reported or could be calculated were included in this review. The details of the inclusion and exclusion criteria are mentioned in [Table 1]. Only articles published in the English language were included.

We conducted comprehensive search in three databases (PubMed, Scopus, and CINAHL) up to January 1, 2017. The search strategy used keywords related to MIH and terms related to study design. The detailed keywords included in the search strategy for all databases are shown in [Table 2]. Additional articles were hand searched in the citation list of the published articles and reviews. The studies from these three databases were imported to Covidence website for the removal of duplicate titles. The remaining articles had their titles and abstracts screened (PKC and YS) to identify studies for inclusion in the systematic review that matched the inclusion and exclusion criteria. Then, the articles were subjected to full-text screening by two reviewers (PKC and YS) where certain articles were excluded with reasons.

Table 2: Keywords included in the search strategy for all three databases (title, abstract, and MeSH terms of papers)

All the articles after full-text screening were subjected to risk of bias assessment using nine item checklist adapted from Hoy et al. [Table 3].[9] Based on the assessment, studies were identified as a high, moderate, or low risk. The risk of bias assessment was done by two trained and calibrated reviewers (YS and HS). Disagreements if any were resolved after discussion with a third reviewer (PKC).

A specially designed data extraction form was used to extract information from each study. Information included were geographic distribution, criteria used for the assessment of MIH, age, and gender distribution of the sample along with prevalence estimates as per gender.

Statistical analysis

Heterogeneity of the studies was assessed using I2 statistic which evaluates the variation other than that of sampling error. A level of >75% indicates a high degree of heterogeneity. Meta-analysis was undertaken using MetaXL Version 5.3 (Epigear international Pty Ltd., Queensland, Australia) plugin of Microsoft excel (Microsoft Office 2010). Pooled prevalence with 95% confidence intervals (CIs) was reported using quality effects model for meta-analysis. It was done taking into account the quality score obtained from the risk of bias assessment tool.[10] The quality scores were converted into quality ranks by dividing each score by the score of the highest scored study.

Results

Search results

The search resulted in a total of 853 publications from the three databases and additional 2 articles from citation lists through manual search. A total of 744 publications were included in the title and abstract screening after the removal of duplicates. Ninety-three publications were assessed for eligibility in full-text screening, and 651 irrelevant publications were excluded. Further, 25 publications were excluded due to wrong study design/outcome (n = 8), letter to the editor (n = 1), and hospital-based study (n = 16). A total of 68 publications were included in the qualitative synthesis out of which seven studies were excluded (secondary data analysis), and only 61 studies were included in the final meta-analysis [Figure 1].

The risk of bias assessment was done for 61 publications out of which two were in moderate risk and the remaining were at low risk. The studies with moderate risk had nonrepresentative population and sampling frame, nonrandom sampling, and nonresponse rates.[4],[35]

Outcome measurement

Two-thirds of the included studies (n = 41) have used EAPD 2003 criteria and one-fifth of them used DDE index for MIH. Two studies have reported custom criteria,[11],[36] and in one study, the criteria were not clearly described.[37] The evaluation criteria by Weerheijm,[28] Koch,[31] Jalevik,[38] Cho,[39] and Kemoli [40] were less commonly used [Table 4].

Five studies have reported that girls have a significant higher predilection for MIH than boys [23],[36],[47],[48],[49] while 41 studies reported no difference between boys and girls. However, nine out of these 46 studies have not reported gender distribution of the sample [15] or gender-wise MIH distribution [18],[21],[25],[28],[31],[34] or both.[17],[23],[24] The girl to boy ratio among the 37 studies ranged from 0.72 to 3.99.[36],[50] In more than half of these studies, girls had a higher prevalence than boys.

Age variation

One out of all the included studies have not specified the age; six of the 61 studies have mentioned only the mean age.[13],[23],[26],[29],[51],[52] The age ranged from 6 to 17 years among the included studies.

Geographical variation

The lowest prevalence was from India (0.48)[3] and the highest was from Brazil (40.16).[4] The highest number of studies (n = 25) were from Europe with a prevalence range from 3.58 to 36.51.[24],[30] This was followed by Asian countries (n = 18; prevalence range 0.48–27.66)[3],[18] and South American countries (n = 9; prevalence range 2.54–40.16).[4],[16] Country-wise distribution revealed that highest number of studies were reported from India (n = 10) with a range from 0.48 to 26.99,[3],[27] nine studies were reported from Brazil with a range from 2.54 to 40.16,[4],[16] and six studies from Germany with a prevalence range from 5.61 to 36.51.[14],[30]

Meta-analysis

Seven publications were excluded [40],[53],[54],[55],[56],[57],[58] as they were secondary analysis, and a total of 61 publications were included in the analysis of pooled prevalence of MIH which yielded 61 prevalence estimates. The overall quality effects model yielded a prevalence of 11.24 (CI = 9.23–13.45) with high heterogeneity among the included publications (I2 = 98.05; CI = 97.18–98.26; df = 60; Cochran's Q = 3080.35; P < 0.001) [Figure 2]. The analysis was not done separately for low and moderate risk studies as the quality rank score was incorporated in the calculation of pooled prevalence of MIH. A sensitivity analysis was performed by excluding each included publication revealed similar prevalence estimates. Doi plot was used to evaluate the possible publication bias. The plot revealed a minor asymmetry which had an Luis Furuya-Kanamori index of 1.74.

Our review aimed to evaluate the pooled prevalence of MIH among children. Sixty-one prevalence estimates constituted to the pooled prevalence of MIH in this meta-analysis. This review evaluated three major databases and only articles in English were included. A hand search of all the included full-text articles was done. We have not attempted to search gray literature. No attempt was made to translate the other language articles as there was a paucity of resources. A minor asymmetry in Doi plot suggested a possible role of publication bias which may not be systematic and can be concluded that the studies represent a reasonable prevalence of MIH among the general population. We used a quality assessment tool that was developed and modified by Hoy et al. in 2012.[9] It was reported to be easy to use tool with good reliability. To eliminate any chance of subjectivity in the quality assessment, two calibrated reviewers performed the exercise with minimal disagreements.

The prevalence estimates were calculated based on the information from the publications, and no attempt was made to contact the individual authors for the data. Although there was a lot of variation with respect to the criteria that was used for the assessment of MIH, EAPD 2003 was the most acceptable criteria.[1] However, we included all the studies irrespective of the working definition for diagnosis of MIH because all the studies used the criteria for MIH prevalence that was based on its presence on molars. Considering the variation and heterogeneity among the included studies, the estimates that were presented have to be interpreted with caution.

Geographic variation in the prevalence of MIH was evident with a lower prevalence in Asian countries when compared with European and South American countries. No study was reported from North American countries. The highest prevalence estimate was from Brazilian middle social class school children [4] whereas the lowest prevalence estimate was of Indian urban school children.[3] A total of 41 publications reported a higher prevalence in girls than boys and five publications reported that the difference was statistically significant. Overall, we can conclude that the prevalence of MIH was 11.24% with a high degree of geographic variation and mild variation with respect to gender. High-quality prevalence studies are required, and emphasis should be on presentation of prevalence figures based on age and gender.

Conclusion

Our review showed the prevalence of MIH along with heterogeneity in the studies and minimal risk of publication bias among the published studies. MIH is a major problem, and one in ten children among general population might be affected. It can cause far-reaching complications for both the child and the dentist. Dentists should be aware of this common problem, and early diagnosis and preventive management can help to delay or intercept the complications such as posteruption breakdown, sensitivity, and caries. Non-English publications were not included; high heterogeneity and publication bias were some of the limitations of this review. Further studies should incorporate the prevalence estimates based on the widely accepted EAPD criteria. Future studies on the prevalence of MIH should incorporate the distribution of the same with respect to gender, age, and demographic variables to further understand the role of these factors. [75]

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Temilola OD, Folayan MO, Oyedele T. The prevalence and pattern of deciduous molar hypomineralization and molar-incisor hypomineralization in children from a suburban population in Nigeria. BMC Oral Health 2015;15:73.